A tactile sensor and a method of manufacturing thereof

ABSTRACT

A capacitive or resistive tactile sensor having a conductive membrane, a flexible dielectric or weakly conductive sheet and a substrate having electrodes, and a method of manufacturing thereof. The flexible sheet has a first surface and an opposite second surface, the first surface and the second surface are uniformly distanced when at rest. The first surface is adapted to contact one of the conductive membrane or the substrate. The second surface is adapted to contact another one of the conductive membrane or the substrate. The body defines between the first and second surfaces, at a predetermined region, a plurality of laser ablated uniform cavities that are evenly distributed and operatively identical in order to provide a known compression index at the predetermined region of the flexible sheet. The substrate has uniformly distributed static pressure sensing electrodes and at least one uniformly spread dynamic pressure sensing electrode, which is located between the static pressure sensing electrodes, and is used for measuring a voltage or a current variation with the conductive membrane according to the deformation of the flexible sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. provisional patent application62/445,394, filed Jan. 12, 2017, the content of which is herebyincorporated by reference.

TECHNICAL FIELD

The present relates to tactile sensors and methods of manufacturingtactile sensors. More specifically, the present relates to dielectricsor to weakly conductive material and conductive plates in capacitive orresistive tactile sensors and to methods of manufacturing dielectrics orto weakly conductive material.

BACKGROUND

As robots have gained importance in the field of manufacturingprocesses, so in parallel greater automation has been achieved thanks tonew technologies. At the beginning of the robotic era, robotic gripperswere used in straightforward manufacturing tasks such as for carassembling tasks. However, today robotic grippers must do more than justgrasp a same item or similar items repeatedly. Indeed, robotic grippersare expected to be capable of handling complex objects that may have avariety of different shapes, or be made of unstructured fabrics orfragile materials. Robots are now expected to have some “sense” of howto accomplish a manufacturing task and successfully handle a variety ofobjects without damaging them.

The human hand, with its various mechanoreceptors, remains thebest-functioning “device” for object-manipulation tasks. In an attemptto replicate these functions robotically, researchers have developedtactile sensors based on numerous different sensing principles, such asby using piezoresistive rubber, conductive ink, piezoelectric material,conductive fluid, and measuring a change in capacitance. Most of theseapproaches are about measuring a contact pressure. However, the humansense of touch does not rely on contact pressure alone. It also usesvibration, temperature, and shear loading, among others. Theseadditional modalities let humans recognize surface texture, detectobject slippage, and perceive other complex events. With this in mind,some researchers in robotics are now building multimodal tactile sensorsin hopes of giving robots a sense of touch that is more similar to thehuman one. Along with detecting pressure localization and magnitude,these modern sensors can also detect contact events like vibration. Forexample, some have developed a variable resistor ink sensor that canalso detect incipient slip thanks to the use of Polyvinylidene fluoride(PVDF). Others have developed a multimodal sensor for fabricmanipulation and classification.

One well-known multimodal sensor is the commercially-available BioTac™tactile sensor provided by SynTouch LLC and described in U.S. Pat. Nos.7,658,119, 8,181,540, and U.S. Pat. No. 8,272,278 to Loeb et al. TheBioTac™ tactile sensor can measure vibrations in addition to temperatureand pressure. The tactile sensor has a conductive plate with multipleelectrode points arranged in a two-dimensional array such as presentedin Prior Art FIG. 1. Each electrode point 100 is connected to animpedance measuring circuitry 102, and is surrounded by a weaklyconductive fluid or pulp contained within an elastomeric skin. When anexternal force is applied to the skin, a variation in the fluid pathsaround the electrode points produces a distributed pattern of impedancechanges indicative of information about the forces and objects thatapplied them. In one example, the impedance measuring circuitry isconfigured to detect changes in the electrical impedance of the volumeconductive liquid between the electrodes, and to interpret such changesunder certain circumstances as being indicative of a shear force that isapplied to the skin. The tactile sensor is thereby able to measuremicro-vibrations due to sliding friction, as well as to measurepressure. A same electrode 100 is used for providing a micro-vibrationmeasurement and a pressure measurement. The electrodes are alternatinglyconnected to a vibration sensing subsystem and to a pressure sensingsubsystem. A multiplexer 104 selects each electrode in turn forconnecting to one of the vibration sensing 106 or pressure sensing 108measuring circuitries, according to instructions received by amicrocontroller 110.

As can be noticed from these sensors, sensors for grasping applicationsneed to be capable of more than simply the ability to sense forces.However, the aforementioned sensors require the use of special materialsand complex structures that can be difficult to assemble, fabricate, andmaintain. In particular, the Bio Tac™ sensor requires a specializedtechnician to inject a fluid under the skin, which can result in somedowntime since the skin of the sensor can wear out frequently. Moreover,the BioTac™ sensor requires a whole phalange to be replaced in order forit to be integrated with a robotic hand.

Other solutions have been developed to provide multimodal sensing. Onesolution relates to capacitive sensing. Capacitive sensors appear to bea suitable candidate for multimodal tactile sensing due to theirsimplicity and easy-to-implement properties. The performance of acapacitive sensor depends on its electrical circuit and theelectro-mechanical characteristics of its dielectric. Researchers havedeveloped capacitive sensors that can perform both static and dynamicsensing by using to integrated circuits (ICs) that enable the sensor'selectronic circuit to process the additional data needed for dynamicsensing. As a result, such sensors are capable of classifying varioustypes of contact events.

It has been shown that by cleverly designing the dielectric, thesensor's sensitivity can be greatly enhanced. Several researchers havesucceeded in improving the sensitivity of their capacitive sensors byusing dielectrics made of elastomer foam and microstructured rubber.Another research group attained extremely high sensitivity using amicrostructured dielectric made of nanoparticle-filled elastomer, suchas presented in Prior Art FIG. 2A. The sensor 200 has a pair of spacedapart conductive plates 202 with a dielectric 204 there between. Thedielectric 204 has a microstructure of a plurality of protrusions 206conductively extending between the two conductive plates 202. Eachprotrusion 206 has at least two layers 208 and 210. The first layer 208having a greater diameter than that of the second layer 210 accounts forsignificant variations between the two plates 202 and reacts to greaterpressure ranges. The second layer 210 accounts for weaker variationsbetween the two plates 202 and reacts to lower pressure ranges. However,these highly sensitive capacitive sensors are inconvenient andtime-consuming to manufacture due to the specialized dielectricfabrication processes.

In US Patent Publication No. 2015/0355039 to Duchaine et al. there ispresented a method of using invert molding to cast the dielectric out ofliquid elastomer filled with nanoparticles. The casted dielectric has adielectric constant of 12. Prior art FIG. 2B depicts the various stepsin manufacturing the dielectric. A mold is first provided and is filledwith liquid elastomer filler. A conductive fabric is then placed incontact with the filler before curing. Once cured, the combination ofthe molded dielectric and the conductive fabric is removed from themold. Prior art FIG. 2C presents a magnified view of the moldeddielectric 204. As can be noticed, each protrusion 206 of the moldeddielectric 204 has a different shape, and the dielectric does notprovide a consistent thickness. Moreover, the method is verytime-consuming due to the invert molding process and cannot be appliedin mass production of sensors, since the molding process can takeseveral days.

SUMMARY

According to one aspect, there is a method of manufacturing acompressible sheet made from a dielectric material or a weaklyconductive material for a sensor. The sensor being adapted to measureeither a localized change in capacitance or conductivity correspondingto an applied pressure on the compressible sheet. The method includes,positioning a flexible sheet made from a dielectric material or a weaklyconductive material in a laser ablation machine. The method furtherincludes determining a least one ablation path according to a desiredpattern of cavities and according to a size and a shape of each cavityof the desired pattern of cavities, and adjusting parameters of thelaser ablation machine according to the at least one ablation path andat least one property of the flexible sheet. Then ablating the flexiblesheet with the ablation machine according to the adjusted parameters andforming the compressible sheet having a body structure that iscomplementarily shaped according to the desired pattern of cavities, andremoving ablation debris from the body structure. The body structure isadapted to provide a localized compression such that when thecompressible sheet is subjected to a localized pressure, an associatedportion of the body structure is locally deformed only by at leastpartially extending into adjacent cavities, according to a deformationratio that is indicative of the capacitance or resistance of thecompressible sheet at the location of the localized pressure.

It has been found that laser ablation of a suitable material can lead tobetter compressibility properties than by molding a moldable materialwith suitable feature dimensions.

According to another aspect, there is a dielectric or weakly conductivecompressible sheet for a capacitive or resistive tactile sensor. Thesheet is positionable between a conductive membrane and a conductiveplate of the tactile sensor. The compressible sheet has a body having afirst surface and an opposite second surface, the first surface and thesecond surface is uniformly distanced when at rest. The first surface isadapted to contact one of the conductive membrane or the conductiveplate. The second surface is adapted to contact another one of theconductive membrane or the conductive plate. The body defines betweenthe first and second surfaces, at a predetermined region, a plurality oflaser ablated uniform cavities that are evenly distributed andoperatively identical in order to provide a known compression index atthe predetermined region of the compressible sheet.

According to another aspect, there is a substrate for a tactile sensor.The substrate has a dielectric contacting surface, a plurality of staticpressure sensing electrodes and at least one dynamic pressure sensingelectrode. The plurality of static pressure sensing electrodes areuniformly distributed on the dielectric contacting surface. Each of theplurality of electrodes are adapted to connect to a corresponding one ofa plurality of static pressure processing circuits. The at least onedynamic pressure sensing electrode is uniformly spread across thedielectric contacting surface between the plurality of static pressuresensing electrodes. Each of the at least one electrode is adapted toconnect to at least one corresponding dynamic pressure processingcircuit.

According to another aspect, there is a capacitive or resistive tactilesensor having a conductive membrane, a laser ablated dielectric orweakly conductive sheet, a conductive plate. The conductive membrane isconnected to a ground or to a power source and adapted to deformaccording to an external pressure application. The laser ablateddielectric or weakly conductive sheet has a body with a first surfaceand an opposite second surface. The first surface is in contact with theconductive membrane and is adapted to deform according to the externalpressure application in conjunction with the conductive membrane. Theconductive plate has a pattern of electrodes for measuring a voltagevariation or a current variation with the conductive membrane accordingto the deformation of the laser ablated sheet. The second surface isadapted to directly contact the conductive plate. The body definesbetween the first and second surfaces, at a predetermined region, aplurality of uniform laser ablated cavities that are evenly distributedand operatively identical in order to provide a known compression indexat the predetermined region of the compressible sheet.

According to another aspect, there is a method of manufacturing adielectric sheet for a capacitive tactile sensor. The method includespositioning a dielectric sheet in a laser cutting machine, adjusting aprobe height of the laser cutting machine according to a thickness ofthe dielectric sheet and a preset laser beam focal point distance,etching the dielectric sheet, retrieving the etched dielectric sheet,and removing etching debris from the etched dielectric sheet. Theetching includes controlling a displacement and velocity of the probe,according to a predetermined etching pattern and according to thepositioning of the dielectric sheet. Moreover, the etching includescontrolling a power and frequency of a laser beam focused by the probeonto the dielectric sheet, according to the predetermined etchingpattern, in order to form in the dielectric sheet a first region that isfull and a second region that defines a plurality of protrusions.

According to another aspect, there is a particular geometry of adielectric sheet for a capacitive tactile sensor. The dielectric sheetis positionable between a conductive sheet and a conductive plate of thecapacitive sensor. The geometry of the dielectric sheet includes auniform surface, and a dented surface that is opposite to the uniformsurface. The uniform surface is adapted to contact either the conductivesheet or the conductive plate. The dented surface is adapted to contactthe other one of either the conductive sheet or the conductive plate.The dented surface defines a plurality of frustoconical projections thatare evenly distributed and operatively identical. Each of the pluralityof frustoconical projections has a base and a truncated tip that issmaller in diameter than the base, the truncated tip is adapted todirectly contact the other one of the conductive sheet or the conductiveplate.

According to another aspect, there is a capacitive tactile sensor. Thecapacitive tactile sensor has a conductive sheet, a dielectric sheet,and a conductive plate. The conductive sheet is connected to a groundand is adapted to deform according to an external pressure application.The dielectric sheet has a uniform surface and an opposite dentedsurface, one of the surfaces is in contact with the conductive sheet andis adapted to deform according to the external pressure application inconjunction with the conductive sheet. The conductive plate has apattern of electrodes for measuring a voltage variation with theconductive sheet according to the deformation of the dielectric sheet.The dented surface defines a plurality of frustoconical projections thatare evenly distributed and operatively identical, each of the pluralityof frustoconical projections has a base and a truncated tip that issmaller in diameter than the base, the truncated tip is adapted todirectly contact the other one of the conductive sheet or the conductiveplate.

According to yet another aspect, there is a conductive plate for acapacitive tactile sensor. The conductive plate has a dielectriccontacting surface adapted to contact a dielectric, and an electricallyinsulated surface opposite the dielectric contacting surface. Thedielectric contacting surface has a plurality of static pressure sensingelectrodes and at least one dynamic pressure sensing electrode. Theplurality of static pressure sensing electrodes are uniformlydistributed on the dielectric contacting surface. The at least onedynamic pressure sensing electrode is uniformly spread across thedielectric contacting surface between the plurality of static pressuresensing electrodes. Each of the plurality of electrodes is adapted toconnect to a corresponding one of a plurality of static pressureprocessing circuits and each of the at least one electrode is adapted toconnect to at least one corresponding dynamic pressure processingcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 presents a prior art conductive plate system for sensing staticand dynamic pressure;

FIG. 2A presents a prior art side sectional view of a tactile sensorhaving a conductive sheet, a dielectric sheet and a conductive plate;

FIG. 2B presents a prior art method of manufacturing the dielectricsheet of FIG. 2A;

FIG. 2C presents a prior art magnified view of molded protrusions of aportion of the dielectric sheet manufactured by the method presented inFIG. 2B;

FIG. 3A presents a side sectional view of a tactile sensor having aprinted circuit board, conductive film, a dielectric sheet and aconductive fabric, according to one embodiment;

FIG. 3B presents a side sectional view of the tactile sensor of FIG. 3Ahaving applied thereon various pressure levels, according to oneembodiment;

FIG. 4 presents a top view of the dielectric sheet of FIG. 3A, accordingto one embodiment;

FIG. 5 presents a schematic side view of a laser etching machine havinga uniform dielectric sheet placed therein for producing the dielectricsheet of FIG. 3A, according to one embodiment;

FIG. 6 presents a block diagram of a method of producing the dielectricsheet of FIG. 3A, according to one embodiment;

FIG. 7A presents a top view of the printed circuit board of FIG. 3A, theprinted circuit board defining a pattern of electrodes for integratedstatic and dynamic pressure measurement, according to one embodiment;

FIG. 7B presents a top view of the printed circuit board of FIG. 3A, theprinted circuit board defining a pattern of electrodes for integratedstatic and dynamic pressure measurement, according to an alternateembodiment;

FIG. 8 presents a tactile capacitive sensor having the dielectric sheetand the printed circuit board of FIG. 3A and a sectional view drawingthereof, according to one embodiment; and

FIG. 9 presents an illustration of a robot gripper equipped with thetactile sensor of FIG. 8 and holding a tool while showing a pressure mapgenerated using the tactile sensor.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

Presented in FIG. 3A is a partial sectional view of a capacitive tactilesensor 300 adapted to transfer a pressure applied on a contact surfaceterminal 302 towards a pressure detector terminal 304, according to oneembodiment. The contact surface terminal 302 is a conductive membranesuch as a conductive fabric layer that is electrically grounded forshielding the sensor 300 from external noise. The pressure detectorterminal 304 is a conductive plate such as a printed circuit board (PCB)having electrodes adapted to measure a capacitance between theelectrodes and the contact surface terminal 302. Between the contactsurface terminal 302 and the pressure detector terminal 304 there is acompressible dielectric sheet 306. As presented in FIG. 3B, thedielectric sheet 306 is adapted to compress according to pressureapplied to the contact surface terminal 302, and thereby to modify thecapacitance between the contact surface 302 and the pressure detectorterminal 304. In the embodiment of FIG. 3A, a high dielectricpermittivity material 308 such as a polyvinylidene difluoride (pvdf)film is applied over the pressure detector terminal 304 in order toenhance the sensor 300 response. The pvdf film is a non-piezoelectricfilm, however the pvdf film can be replaced by a piezoelectric pvdf filmwithout departing from the scope of the present sensor. Moreover, askilled person would understand that depending on the sensor 300, insome applications the high dielectric permittivity material 308 may notbe required, for instance in low force range applications where thedielectric sheet 306 is often thinner.

Moreover, it shall be understood that the dielectric sheet could bereplaced by a compressible electrically conductive sheet made from aweakly conductive material such as silicone filled with carbon particlesor an optical material that is electrically conductive, when used insensors that measure a change in electrical resistance such as in aresistive sensor or a change in optical properties. According to oneembodiment, an electrically conductive membrane connected to a currentsource such as a DC source is placed between the contact surface 302 andthe electrically conductive sheet The electrically conductive sheet isadapted to compress according to pressure applied to the contact surfaceterminal 302, and thereby to modify the resistance between the contactsurface 302 and the pressure detector terminal 304. The pressuredetector terminal 304 is a printed circuit board (PCB) having electrodesadapted to measure a resistance between the electrodes and the contactsurface terminal 302.

Dielectric Sheet

As further presented in FIGS. 3A and 3B, according to one embodiment,the dielectric sheet 306 has a first region 310 that is full and asecond region 312 that defines a plurality of protrusions 314 that aresimilar in shape or, at least macroscopically, identical in shape. Eachprotrusion 314 has a frusto-conical shape, as better shown in FIG. 4.When a pressure is applied to a given location of the contact surfaceterminal 302, a set of corresponding protrusions 314 are accordinglycompressed towards the detector terminal 304, locally reducing the spacebetween the contact surface terminal 302 and the detector terminal 304and accordingly modifying the capacitance there between. The detectorterminal 304 is adapted to locally measure the capacitance andvariations of the capacitance in order to detect localized pressureapplied to the contact surface terminal 302.

Notice from FIG. 3B that upon a localized pressure application on thecontact surface terminal 302, a corresponding set of protrusions 314 arecompressed by expanding into adjacent cavities and the localizedpressure does not increase a thickness of portions of the dielectricsheet 306 that surround the localized pressure. As a result, thedielectric sheet is adapted to provide a localized compression such thatwhen the compressible dielectric sheet is subjected to a localizedpressure, an associated portion of its body is locally deformed only byat least partially extending into at least one adjacent cavity,according to a deformation ratio that is indicative of the capacitanceor resistance of the compressible sheet at the location of the localizedpressure.

It shall be recognized that although the sensor 300 depicted in FIG. 3A,presents the dielectric sheet 306 with the protrusions 314 orientedtowards the detector terminal 304, the dielectric sheet 306 could beflipped and the protrusions 314 could be oriented towards the contactsurface terminal 302.

The dielectric sheet 306, and more particularly the flexibility, thedisposition, shape and dimensions of the protrusions 314, allows thedetector terminal 304 to detect pressures ranging from 0 Newtons to atleast 50 Newtons applied to an area as small as 126 square millimeters(mm²) with an accuracy 1·10⁻⁴ Newtons when placed on a detector terminal304 with electrodes each having a surface ranging between 6.25 mm² and16 mm², according to one embodiment

According to one embodiment, the protrusions as presented in FIG. 4,have width at a base 402 that is less than 1 mm are spaced apart by adistance of less than 1 mm. In another embodiment, the protrusions havea width at a base 402 that is less than 0.8 mm and are spaced apart by adistance of less than 0.8 mm. In yet another embodiment, the protrusionshave a width at a base 402 that is less than 0.6 mm and are spaced apartby a distance of less than 0.6 mm and provide 87 protrusions within anarea of 126 mm², namely a density of approximately more than 25 persquare centimeter, preferably more than 40 protrusions per squarecentimeter, and more preferably more than 60 protrusions per squarecentimeter. The recited ranges for protrusion dimensions and densitylikewise can apply correspondingly for the dimensions of the structuresof cell walls and cavities.

It shall be recognized that the pressure ranges detected by the terminal304 depend on the flexibility of the dielectric material, the shape anddimensions of the protrusions or the pattern of cavities ablated in thedielectric material.

It shall further be recognized that the dielectric material is flexibleand following an ablation process the ablated dielectric materialdefines protrusions that are highly compressible. According to oneembodiment the dielectric is a flexible urethane material made from aurethane resin having a dielectric constant ranging between 4 and 6 anda Shore Hardness ranging between 00-30 to A-60 (e.g. Extra Soft toSoft).

According to one embodiment, as further presented in FIG. 4, eachprotrusion has a base 402 measuring 0.6 mm in diameter, a flat tip 404measuring 0.3 mm in diameter, and a height measuring 0.5 mm. In thisembodiment the protrusions are equidistantly distributed on thedielectric sheet 306 according to a square grid configuration and adistance or pitch between each protrusion measures 1.2 mm. However,those parameters can vary depending on the desired sensor 300performance or sensitivity.

A skilled person will recognize that the dimensions of each protrusion314 can differ from the embodiment presented in FIG. 4. Moreover, theprotrusions 314 of FIG. 4 have identical dimensions, however, it shallbe recognized that the protrusions can have variable controlleddimensions, depending on their position on the dielectric sheet 306. Forinstance, two types of protrusions 314 can be sequentially distributedon the dielectric sheet 306, a first type of protrusion 314 beingshorter in height or wider at the base 402 or the tip 404 than a secondtype of protrusion 314. In another instance, two types of protrusions314 can be distributed according to a portion of the dielectric sheet306, a portion of the dielectric sheet 306 such as a center portion, acorner portion or a half portion can have distributed protrusions thathave different dimensions then those distributed in a remaining portionof the dielectric sheet 306. The types of protrusions shall not belimited to one of two types of protrusions, a plurality of types ofprotrusions can be controllably dimensioned and distributed in thedielectric sheet 306, without departing from the scope of the presentdielectric sheet 306.

A skilled person will also recognize that the protrusions could bedistributed differently on the dielectric sheet 306, than in the squaregrid distribution of FIG. 4. Indeed, the protrusions 314 can bedistributed according to any controlled configuration. For instance, theprotrusions 314 can be distributed in a circular configuration, in astaggered configuration or in any other suitable configuration.

Moreover, the distance between each protrusion can differ from oneapplication to another and can also be variable depending on theconfiguration of the protrusion distribution.

Also, it shall be recognized that the that the protrusions can have adifferent shape and can be part of a compressible body structure definedby cavities that have been ablated. The compressible body structure candefine walls forming cells having a circular shape, a conic shape, ahoneycomb shape or any other suitable shape. The cells can be open orenclosed within the surfaces of the dielectric sheet.

Method of Producing the Dielectric Sheet

According to one embodiment and as presented in FIG. 5, a conventionallaser etching machine 500 is used to ablate, cut or engrave theprotrusions 314 from a conventional flexible or soft dielectric material502 having an uniform thickness. This laser etching machine 500 has aprobe 504 adapted to direct a laser beam onto the flexible dielectricmaterial 502. The probe 504 is displaceable along a horizontal rail 506and a vertical rail 508 and displacement along both axes is therebyprovided. The displacement of the probe 504 is programmable according toan ablation path and adapted instructions are provided to the laseretching machine 500 to produce a desired pattern of protrusions orcavities and produce the compressible dielectric sheet 306. The distancebetween the cutting surface 510 and a light emitting head 505 of thelaser probe 504 is adjustable along an elevation rail 507. In thisembodiment the cutting surface 510 is slideably mounted on the elevationrail 507 and the distance between the light emitting head 505 and thecutting surface 510 is thereby adjusted. This distance parameter iscritical to the geometry of the protrusions 314. A dielectric sheet 502will not be etched or cut if it is out of focus with respect to thelaser probe, such as when the dielectric sheet 502 is too far away fromthe light emitting head 505, therefore the laser machine 500 must beadjusted according to the properties of the dielectric sheet 502 and theablation path. The laser etching or ablation machine can be, forexample, a CO2 laser cutter or an Nd:YAG laser for surface ablationallowing to produce cavities in the sheet, and subsurface ablation canalso be performed. Whether the resulting material has protrusions on oneside (or both), an open cellular structure on one side, an open cellularstructure throughout the material, or closed cells, the material iscompressible in response to the applied pressure. Laser processing ofthe sheet can provide the precision required for the texturing orstructuring of the sheet material that is required for spatially uniformtactile sensitivity. The resulting texturing of the sheet surface can beprotrusions 314 or cavities between a continuous “cellular” wallstructure.

Moreover, according to a predetermined distance of the head 505 withrespect to the uniform dielectric material 502 (i.e. referencecoordinates of the probe), a laser power setting and probe speed settingare also provided in order to control the diameter, the pitch, and theheight of each protrusion 314. A laser power setting that is too strongor a probe speed that is too slow will cut through the uniformdielectric material 502. A laser power setting that is too low or aprobe speed that is too fast will produce protrusions 314 that are tooshort. Once the required parameters for the laser power and probe speedare determined for the desired etching pattern the laser etching machinecan repeatably produce numerous suitably identical dielectric sheets 306within a short period of time, as presented in FIGS. 4 and 5, withouthaving to resort to lengthy molding or casting methods.

According to one embodiment as presented in FIG. 6, there is a method600 of producing the dielectric sheet 306 for the capacitive tactilesensor 300, as concurrently presented in FIG. 3A. The method 600consists of positioning 602 the uniform dielectric material 502 onto acutting surface 510 of the laser cutter 500, as concurrently presentedin FIG. 5. The dielectric material 502 must previously have been chosenaccording to the desired application with respect to various propertiesof the material such as the dielectric permittivity, the thickness andthe hardness. The sensor 300 having to measure a wide range of forcesmight require a dielectric material 502 that is thicker and harder thanthe sensor 300 having to measure a lower range of forces with howevergreater precision. Indeed, the thicker the material 502, the larger themeasureable force range but the lower the measurement precision (i.e.lower response rate). Also, the softer the material 502, the higher themeasurement precision but the lower the saturation threshold. Moreover,the shape and dimensions of the dielectric material 502 must be adaptedor adaptable to the shape and dimensions of the sensor 300.

The method 600 further consists of defining a laser probe path 604according to a predetermined microstructure pattern to be cut forcreating a desired distribution of protrusions 314 on the dielectricmaterial 502. The predetermined microstructure pattern indicates thetype of distribution of the protrusions 314 (i.e. grid, circular,staggered, etc.), the protrusion 314 density or resolution (i.e. spacebetween protrusions or pitch), and the geometry of the protrusions 314(i.e. base diameter, flat tip diameter and height).

The method 600 further consists of setting the cutting parameters 606depending on the uniform dielectric material 502 and the characteristicsof the laser etching machine 500. For instance, the laser power andprobe speed must be adjusted according to the dielectric material, themicrostructure pattern to be cut, and the distance between the probehead 505 and the dielectric material 502.

The method 600 further consists of adjusting the probe head distance 608with respect to the cutting surface 510 according to a predeterminedreference height. The probe head distance is adjusted according to thepredetermined reference height but also according to an offset resultingfrom the support of the dielectric material 502. The support is neededin order to prevent unwanted overheating of the material 502 when placedon the cutting surface 510.

The method 600 further consists of cutting 610 the uniform dielectricmaterial 502 according to the previously set parameters in order toproduce the dielectric sheet 314.

Once produced, the dielectric sheet 314 is removed 612 from the cuttingsurface 510 and any excess fluids (i.e. melted by-product of thedielectric material 502) produced by the cutting is removed during apost-processing 614 of the dielectric sheet 314.

It shall be recognized that the method 600 of FIG. 6 is adapted toproduce a single dielectric sheet but is also adapted to produce aplurality of dielectric sheets. Indeed, the setting of the cuttingparameters 606 can be adapted to produce more than one dielectric sheetand the cutting 610 of the uniform dielectric material 502 can includethe cutting through the uniform dielectric material 502 at a perimeterregion of the dielectric sheet 314 in order to produce severaldielectric sheets from a single dielectric material 502. Also thepost-processing 614 can include the separation of dielectric sheets 314.

The production of a plurality of dielectric sheets 314 at once, enablesproducing a greater number of dielectric sheets within a given period oftime. In addition to being highly accurate and repeatable, the presentmethod allows to increase dielectric sheet generation productivity.

Moreover, it shall be recognized that the method of producing adielectric sheet 600 of FIG. 6 can be repeated as needed. According toone embodiment of the method 600, the laser probe path is pre-defined,the cutting parameters are preset and the laser probe distance isadjusted in advance. The method 600 only includes positioning theuniform dielectric material 602 onto the cutting surface 510, cuttingthe uniform dielectric material 610, removing the produced dielectricsheet 612 and post-processing the dielectric sheet 614. The uniformdielectric material being positioned onto the cutting surface 510 thathas been adjusted in advance with respect to a required laser probedistance. The uniform dielectric material being cut 610 according to thepre-defined laser probe path and preset cutting parameters.

Pressure Detector

According to one embodiment, presented in FIG. 7A is a conductive plate700 of the detector terminal 304, as concurrently presented in FIG. 3A.The conductive plate 700 is a form of substrate such as a PrintedCircuit Board (PCB) that defines a grid-like pattern of electrodes andis adapted to provide integrated static and dynamic sensing of pressure.The grid-like pattern of electrodes includes a number of static pressuresensors 702 connected to a static pressure processor 703, and a singledynamic pressure sensor 704 connected to a dynamic pressure processor705. The integrated static and dynamic sensors (702 and 704) arepositioned to contact the high dielectric permittivity material 308 ordirectly contact the dielectric sheet 306. The static sensors 702 areadapted to provide pressure measurements for localizing an appliedpressure such as a normal pressure or a shear force. The dynamic sensor704 is adapted to provide pressure change measurements for detecting acontact event such as slippage or object recognition. According to oneembodiment, the static sensors 702 are square shaped electrodes ortactile pixels (taxels) that are adapted to take static pressuremeasurements. The dynamic sensor 704 is a single grid shaped electrodethat is adapted to take dynamic pressure measurements over the surfaceof the detector terminal 304. The static sensors 702 are disposed on asame surface as the detector terminal 304 in an array configuration soas to be in an integrated arrangement with the dynamic sensor 704, asbetter shown in FIG. 7A.

In the embodiment of FIG. 7A, the static sensors 702 are an array oftwenty-eight tactile pixels (taxels) arranged on the detector terminal304 or printed circuit board (PCB) measuring 22 mm×37 mm. Each staticsensor 702 is an individual square measuring 3.625 mm×3.625 mm. When apressure is applied to a given region of the contact surface 302, adisplacement of the dielectric sheet 306 occurs at a portioncorresponding to the given region. A change in the capacitance at ataxel 702 or group of taxels 702 adjacent to the portion of thedielectric sheet 306 is measured and a mapping of the capacitancemeasurement at each taxel 702 indicates where the pressure has beenapplied. Each taxel electrode 702 can be provided with a via in the PCBto be connected to the processor 703. It will be appreciated thatbetween electrodes 702 and the at least one electrode 704, an insulatinggap or material is provided. The surface area occupied by the insulationreduces overall sensitity.

The dynamic sensor 704 presented in FIG. 7A is adapted to measure avariance in capacitance irrespective of where the change in pressureoccurred. The localization of the pressure being provided by the staticsensors 702, when a variance in pressure is detected, the localizationof the change in pressure is determined by the measurement provided byat least one of the static sensors 702.

The combination of the dynamic sensor 704 and the static sensors 702 ona single layer of the conductive plate is adapted to detect a dynamicpressure and a static pressure simultaneously. According to pie-chart706 of FIG. 7A, forty-five percent of the detector terminal 304 surfaceis adapted to detect a static pressure, forty-two percent of thedetector terminal 304 surface is adapted to detect a dynamic pressure,and the balance of thirteen percent is attributed to a lost area that isoccupied by the insulation present between the electrodes 702 and 704.As can be noticed, the surface for detecting a static pressure and thesurface for detecting dynamic pressure are relatively equal—betweenforty-two and forty-five percent.

According to an alternate embodiment of the detector terminal 304,presented in FIG. 7B is a conductive plate 710 defining an interlacedpattern of electrodes adapted to provide integrated static and dynamicpressure readings. According to one embodiment, wave shaped electrodes712 are individually adapted to take static pressure measurements, and acomb shaped electrode 714 is adapted to take dynamic pressuremeasurements over the surface of the detector terminal 304. The waveshaped electrodes 712 and the comb shaped electrode 714 are interlacedand provide a relative equal distribution of static pressure readingsand dynamic pressure readings on the terminal 304. For instance, aspresented by pie-chart 716, thirty-one percent of the terminal surface704 is occupied by the wave shaped electrodes 712, and thirty-ninepercent of the terminal surface 704 is occupied by the comb shapedelectrode 714. The balance of thirty percent being attributed to a lostarea that is occupied by the insulation present between the electrodes702 and 704. Even though a greater space is attributed to the lost areathan in the conductive plate 700 of FIG. 7A, the dynamic pressure andthe static pressure are still detectable at a relatively equalproportion—about thirty percent.

Presented in FIG. 8 is an assembled capacitive tactile sensor 800 and asectional view drawing of the assembled capacitive tactile sensor 800,according to one embodiment. The assembled tactile sensor 800 has aprotective casing 802 that is adapted to receive a PCB (Printed CircuitBoard) case 804, on which a PCB 806 is mounted. The PCB 806 has mountedor printed thereon the conductive plate 700 or 710, various electroniccomponents, and Integrated Circuits adapted to simultaneously processstatic pressure and dynamic pressure detected by the static electrodes(702 or 712) and dynamic electrodes (704 or 714) of FIGS. 7A and 7B. ThePCB case 804 is adapted to protect the PCB 806 from bending whilepressure is applied on the sensor 800. The dielectric 306 is placed overthe PCB 806 with the microstructured pattern facing the taxels (702, 704or 712 and 714). The conductive fabric 302 is placed over the dielectric306, which then, together with the conductive plate 700 or 710, formsthe capacitor. The same conductive fabric 302 is used to shield thesensor from environmental electrical noise.

Moreover, a protective layer of silicone rubber 808 covers the sensor800. As can be noticed, the silicone rubber 808 has a crisscross texturein order to promote greater contact friction and facilitate manipulationtasks. The protective casing 802 is made from aluminum and is designedwith a customizable flange to allow the tactile sensor 800 to beinstalled in a variety of different robotic grippers.

The modular design of the tactile sensor 800 makes it easy to service orto replace parts of the sensor 800. Moreover, the materials used tobuild the capacitive tactile sensor 800 being off-the-shelf products,which reduces the cost of manufacturing. The use of off-the-shelfproducts to build the capacitive tactile sensor 800 also provides agreater level of consistency in the materials and therefore greaterconsistency in the manufactured sensors 800.

Applications in Robotics and Manufacturing

The device as illustrated in FIG. 8 can be applied to a robot asillustrated schematically in FIG. 9. A robot gripper equipped with thetactile sensor 800 of FIG. 8 generates a pressure map as shown in FIG.9. The robot controller can interpret the pressure map to determinewhether how the object has been grasped. When the object is not securelyor correctly grasped, the robot controller can release the object andattempt a new grasp. Changes in the pressure map can indicate if thegrip on the object is stable. The dynamic pressure sensor can also sensethe vibration caused by a slipping of an object held by the gripper. Thetactile sensor 800 is thus an integrated part of the robotic system andimproves efficiency and performance of the robotic system so thatmanipulation and control of parts or components by the gripper lead toimprovements in manufacturing of products including the parts orcomponents manipulated by the gripper.

1. A method of manufacturing a compressible sheet made from a dielectricmaterial or a weakly conductive material for a sensor adapted to measureeither a localized change in capacitance or conductivity correspondingto an applied pressure on the compressible sheet, the method comprising:positioning a flexible sheet made from a dielectric material or a weaklyconductive material in a laser ablation machine; determining a least oneablation path according to a desired pattern of cavities and accordingto a size and a shape of each cavity of the desired pattern of cavities;adjusting parameters of the laser ablation machine according to the atleast one ablation path and at least one property of the flexible sheet;ablating the flexible sheet with the ablation machine according to theadjusted parameters and forming the compressible sheet having a bodystructure that is complementarily shaped according to the desiredpattern of cavities; and removing ablation debris from the bodystructure; wherein the body structure is adapted to provide a localizedcompression such that when the compressible sheet is subjected to alocalized pressure, an associated portion of the body structure islocally deformed only by at least partially extending into adjacentcavities, according to a deformation ratio that is indicative of thecapacitance or resistance of the compressible sheet at the location ofthe localized pressure.
 2. The method of manufacturing the compressiblesheet of claim 1 wherein the flexible sheet defines projectionsprotruding from a base portion of the body structure.
 3. The method ofmanufacturing the compressible sheet of claim 2 wherein the projectionshave a frustoconical shape.
 4. The method of manufacturing thecompressible sheet of claim 1 wherein the desired pattern of cavitiesdefines a single cavity.
 5. The method of manufacturing the compressiblesheet of claim 1 wherein the flexible sheet has a plurality of bodyportions that differ in shape or size and each of the plurality of bodyportions provides a known compression index for an associated region ofthe compression sheet.
 6. The method of manufacturing the compressiblesheet of claim 1 wherein the flexible sheet is uniformly distributedwithin the compression sheet and provides a known compression index forthe compression sheet
 7. The method of manufacturing the compressiblesheet of claim 1 further comprising ablating the flexible sheet with theablation machine for defining at least one ablation debris extractionport.
 8. The method of manufacturing the compressible sheet of claim 7wherein the flexible sheet has a layer made from a non-ablatablematerial.
 9. The method of manufacturing the compressible sheet of claim8 wherein the ablation machine is a sub-surface ablation machine.
 10. Adielectric or weakly conductive compressible sheet for a capacitive orresistive tactile sensor, the sheet being positionable between aconductive membrane and a conductive plate of the tactile sensor, thecompressible sheet comprising: a body having a first surface and anopposite second surface, the first surface and the second surface beinguniformly distanced when at rest; the first surface being adapted tocontact one of the conductive membrane or the conductive plate; thesecond surface being adapted to contact another one of the conductivemembrane or the conductive plate; and the body defining between thefirst and second surfaces, at a predetermined region, a plurality oflaser ablated uniform cavities that are evenly distributed andoperatively identical in order to provide a known compression index atthe predetermined region of the compressible sheet.
 11. The compressiblesheet of claim 10 wherein the body is adapted to provide a localizedcompression such that when the compressible sheet is subjected to alocalized pressure, an associated portion of the body is locallydeformed only by at least partially extending into at least one adjacentcavity, according to a deformation ratio that is indicative of thecapacitance or resistance of the compressible sheet at the location ofthe localized pressure.
 12. The compressible sheet of claim 10 whereinthe plurality of laser ablated uniform cavities form projectionsextending from an internal portion of the body to the first surface. 13.The compressible sheet of claim 12 wherein the projections have afrustoconical shape.
 14. (canceled)
 15. (canceled)
 16. (canceled) 17.(canceled)
 18. A capacitive or resistive tactile sensor comprising: aconductive membrane connected to a ground or to a power source andadapted to deform according to an external pressure application; a laserablated dielectric or weakly conductive sheet having a body with a firstsurface and an opposite second surface, the first surface being incontact with the conductive membrane and being adapted to deformaccording to the external pressure application in conjunction with theconductive membrane; a conductive plate having a pattern of electrodesfor measuring a voltage variation or a current variation with theconductive membrane according to the deformation of the laser ablatedsheet, the second surface being adapted to directly contact theconductive plate; and the body defining between the first and secondsurfaces, at a predetermined region, a plurality of uniform laserablated cavities that are evenly distributed and operatively identicalin order to provide a known compression index at the predeterminedregion of the compressible sheet.
 19. The tactile sensor of claim 18wherein the body is adapted to provide a localized compression such thatwhen the compressible sheet is subjected to a localized pressure, anassociated portion of the body is locally deformed only by at leastpartially extending into at least one adjacent cavity, according to adeformation ratio that is indicative of the capacitance or resistance ofthe compressible sheet at the location of the localized pressure. 20.The tactile sensor of claim 18 wherein the plurality of laser ablateduniform cavities form projections extending from an internal portion ofthe body to the first surface.
 21. The tactile sensor of claim 20wherein the projections have a frustoconical shape.
 22. The tactilesensor of claim 18 wherein the tactile sensor is a capacitive tactilesensor and wherein the conductive plate is a substrate, the substratecomprising: a dielectric contacting surface; a plurality of staticpressure sensing electrodes uniformly distributed on the dielectriccontacting surface, each of the plurality of electrodes being adapted toconnect to a corresponding one of a plurality of static pressureprocessing circuits; and at least one dynamic pressure sensing electrodeuniformly spread across the dielectric contacting surface between theplurality of static pressure sensing electrodes, each of the at leastone electrode being adapted to connect to at least one correspondingdynamic pressure processing circuit.
 23. A method of manufacturing aproduct, the method comprising: providing on a gripper of a robot atactile sensor comprising a dielectric or weakly conductive compressiblesheet as defined in claim 10; using said gripper to grip an object;using at least one of a map of static pressure and a dynamic pressurereading from said tactile sensor to determine at least one of acorrectness and a stability of a grip of said object; changing a grip ofsaid object, if required, as a function of said at least one of acorrectness and a stability of a grip of said object; and using saidrobot to manipulate said object to perform at least one step inmanufacturing said product.
 24. (canceled)